Two-cycle engine



Oct. 11, 1955 s, SHELDRICK 2,720,195

TWQ-CYCLE ENGINE Filed April 16, 1954 INVENTDR ATTORNEY United States Patent TWO-CYCLE ENGINE Laurence S. Sheldrick, Birmingham, Micln, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 16, 1954, Serial No. 423,517

9 Claims. (21. 123--65) ing upon the size of the engine and type of scavenging utilized. Generally in unifiow type scavenging engines,

ithas been found that the most satisfactory scavenging action is obtained by disposing the axes of the intake or admission ports substantially tangential to a circle concentric withand at right angles to the cylinder axes thereby imparting a rotational motion to the air in the horizontal plane. In loop scavenging engines, the admission ports are generally directed towards the side of the cylinder opposite the exhaust ports and various arrangements for aligning the admission ports axes in this general direction are used. In engines of either type, the axes of these ports may be disposed in a plane normal to the cylinder axis or may be directed either upwardly towards or away from the cylinder head and are designed to cooperate with the piston head to obtain the desired motion of the scavenging air.

In the various two-cycle port arrangements, the correct radial angle between the axis of each admission port and a radius bisecting the port has been foundto be a function of the ratio of the width of the port as it enters the cylinder to the length of the port measured axially thereof. Within limits, the less the port width to length ratio, the smaller is the radial angle required for proper air scavenging movement. Consequently, the optimum port is one of substantially rectangular shape having its major dimension disposed axially of the cylinder which permits of a considerable increase of the total port area, the bridge area between the ports, and the piston ring contact area when compared with ports of other shapes. While a substantially rectangular port is of the optimum shape from a design standpoint, it is difiicult to manufacture at the necessary radial angle in a cylinder liner and liners with round ports have achieved wide-spread use, since they are much simpler to manufacture requiring only a simple drilling operation.

An object of this invention is to provide a cylinder for a two-cycle engine with scavenging air admission ports, each equal in scavenging effect to a rectangular port and comprising an opening formed by at least two overlapping circular bores thereby retaining the manufacturing advantage of round ports.

Another object of this invention is to provide a cylinder for a two-cycle engine with scavenging air admission ports, each comprising an opening formed by at least two overlapping circular bores disposed at an angle to each other.

A further object of this invention is to provide a cylinder liner with such scavenging air admission ports formed by overlapping circular bores, each of which is tangentially disposed to a circle within the cylinder.

These, and other objects of the invention will be more thoroughly understood from the following description with referenceto the attached drawing in which:

Figure 1 shows a two-cycle unifiow engine for ilLus-: trative purposes in broken-away section having-a cylinderliner with ports constructed in accordance with my invention.

Figure 2 is an enlarged broken view of liner scavenging air admission ports.

Figure 3 is a cross-sectional view taken along the line 3--3 of Figure 2.

Figure 4 is an enlarged fragmentary view of the portice the cylinder substantially ing shown in Figure 3..

Figure 5 is a fragmentary view of a cylinder liner having a modified form of the ports constructed in accordance with my invention, and

Figure 6 is an enlarged cross-sectional view taken substantially along the line 6-6 of Figure 5.

The engine illustrated in Figure 1 comprises a cylinderv block 1 having a cylindrical bore 2 therein with scavenging air inlet passages as indicated at 3 opening into said bore intermediate its ends. The bore 2 is closed at one end with a cylinder head 4 in which the necessary fuel injectors and exhaust valves are located as indicated at 5 and 6 respectively. A piston is reciprocably mounted within a cylinder liner 8 located within the bore 2.. The cylinder liner 8 is provided with a plurality of scavenging air admission ports 10 my invention; each comprising an opening formed of'at least: two overlapping circular portions. In the illllSa. trated embodiment the two overlapping circularportions' result in ports of substantially figure-eight configuration. The admission ports 10 are controlled by a reciprocable piston 7 and register with the scavenging air inlet passages 3.

The cylinder porting arrangement for a I unifiow scavenged engine shown in Figures 1 to 4 disposes the axes of both the upper and lower portions 11 and 12, respectively, of the ports 10 substantially tangential to a circle within the cylinder liner. The engine shown in Figure 1 is also provided with a gas-valve assembly as indicated at 9 for introducing a gas or more of the admission ports for dual fuel operation.

I In some cases, scavenging in a unifiow engine can be improved by utilizing two or more rows of inlet ports.

having their axes disposed at dilferent radial angles; .the individual port axes of each row of ports being substantially tangential to a circle concentric with and at right angles to the cylinder. The ports of my invention permit this type of porting in a manner not allowed by the conventional single round port. As shown by Figures 5 and 6 the upper and lower portions 11' and 12' of the figure-eight port can be drilled at different angles to achieve this double porting effect. A similar double porting eltect may also be obtained by disposing the overlapping circular portions of the port obliquely of the cylinder axis.

While the invention has been described for use in the admission ports of a particular unifiow two-cycle engine for illustrative purposes, it will be understood that ports formed of overlapping circular portions in accordance with my invention might also be used in a loop scavenged engine for both the admission and exhaust ports and with various alignments of the port axes. In engines of either type, the axes of the circular portions of the ports may be disposed normal to the cylinder axis or may be directed either upwardly towards or away from the cylinder head at either the same, diverging, or converging angles to cooperate with the piston head and the general cylinder design to obtain the desired motion of the scavenging air. It will also be understood that while the ports formed in accordance with my invention have particular utility in two-cycle engines, such ports .constructed in accordance withcharge through one migh also be used in various valve structures and it is fully intended that the claims shall cover such and similar uses of the invention.

1. In a two-stroke cycle internal combustion engine, the'combination comprising a cylinder, a reciprocable piston within said cylinder, and a plurality of admission ports of figure-eight configuration formed in the cylinder and controllable by said piston, each of said ports compfi'sirigtwo overlapping circular portions; the axes of the upper portions of said figure-eight being substantially tmigentialto a first circle concentric to and within the cylinder, and the axes of the lower portions of the admission ports-being substantially tangential to a second circle concentric to and within'the cylinder, said second circle being-of a different diameter from said first circle. 2.1a a two-stroke cycle internal combustion engine, the combination comprising a cylinder, a-reciprocable piston within said cylinder, and a plurality of admission ports of figure-eight configuration formed in the cylinder and controllable by said piston, each of said ports comprisingt'wo" overlapping circular portions; the axes of said admission ports being tangential to a circle concentric to and within the cylinder.

3. Ina two-stroke cycle internal combustion engine, thecombination comprising a cylinder, a reciprocable pistonwithin said cylinder, and a plurality of admission ports f figure-eight configuration formed in the side walls of the cylinder andcontrollable by said piston, each of said ports comprising two overlapping circular portions-the upper portion of each of said figure-eight admission ports being at an angle to. the axis of theirlower'portion.v

A. In .a' two-stroke cycle internal combustion engine, thecombination of a cylinder block having a cylindrical bore therein and a scavenging air inlet passage opening into said bore, a cylinder liner within said bore, a reciprbcablepiston within said cylinder liner, and a plurality ofadmission ports in said cylinder liner registering with said scavenging air inlet passage and controlled by the reciprocable piston, each of said admission ports comprising an opening formed of at least two overlapping circular. portions, saidports defining port bridges therebetween and each of said port bridges having at leastone section intermediate the ends thereof of increased widthdue to'the overlapping circular portions of the adjacent-ports thereby strengthening said port bridges intermediate the ends thereof. I

.5. The combination set forth in claim 4 in which the axes of two of the overlapping circular portions of each port are tangential to a circle within the cylinder liner.

6. The combination set forth in claim 4 in which one of the circular portions of each port opening has an axis tangentially disposed to a first circle within the cylinder and the axis of a second circular portion of each port opening is substantially tangential to a second circle of different diameter within the cylinder liner.

7, A cylinder liner for an engine, said liner having a plurality of closely spaced ports formed circumferentially and intermediate the ends thereof, each of said ports comprising an opening of at least two overlapping circular portions, the axes of the several circular portions of each port being spaced longitudinally of said liner, said ports defining port bridges therebetween and each of said port bridges having at least one section intermediate the ends thereof of increased width due to intermediate the longitudinal ends of each of said port bridges.

.9. A cylinder liner as set forth in claim 7, the axes of the overlapping circular portions of said ports being tangential to a circle within-said liner.

References Cited in the file of this patent VUNITED STATES PATENTS 1,263,820 Tidman Apr. 23, 1918 1,520,620 I Wall Dec. 23, 1924 1,622,717 Hildebrand Mar. 29, 1927 1,728,472 U IBrekke Sept. 17, 1929 2,395,110 Forrest Feb. 19, 1946 FOREIGN PATENTS 507,449- Great Britain June 15, 1939 

